Neuronal cell death induced by DNA damage has been implicated in the pathogenesis of many acute and chronic neurological disorders in humans, and DNA damage-induced cell death is a fundamental principle driving therapy for many types of cancer. The major goal of the experiments in this grant proposal is to determine if DNA damage is a cause or consequence of neurodegeneration. Cultured embryonic mouse cortical neurons will be used as a model to study cause-effect links between specific types of DNA lesions and cell death and the mechanisms of DNA damage-induced apoptosis in young and mature neurons. In Specific Aim 1 we will identify lethal levels of DNA damage in neurons and the relationships between DNA damage level, DNA lesion type, and cell death pattern (apoptosis, necrosis, or hybrid) and will test the hypothesis that toxicity of DNA damaging agents on neurons is maturation-related. We will study if DNA damage occurs preferentially at specific sites within the neuronal genome using comet-FISH analysis. We will identify the major DNA repair and DNA degradation pathways in cortical neurons and will determine whether DNA repair is different in neurons at different stages of maturation. We will test the hypothesis that the dependence of DNA damage-triggered death on caspases and MARK signaling differs in neurons of different maturational states. In Specific Aim 2, we will evaluate upstream mechanisms that link DNA damage to downstream apoptosis mechanisms in cortical neurons. We will test the hypothesis that DNA damage-induced apoptosis in young and mature neurons is mediated by the ATM-p53 or cAbl-p53 signaling networks. In Specific Aim 3, we will determine if enforced expression of DNA repair enzymes that function in base excision repair can be neuroprotective. These experiments will provide important information on the toxicity of DNA damage in neurons, the specific types of DNA damage that can occur in neurons, the effects of DNA damage on neurons of different ages, and the molecular mechanisms that transduce DNA damage signals to apoptotic pathways in neurons. This work is relevant to human disease because it will contribute to the understanding of the pathobiology of DNA damage-induced neurodegeneration and to the identification of possible molecular targets for reducing the toxic and neurologic side-effects of cancer therapy.